Boiler operation method and boiler

ABSTRACT

A boiler according to the present invention is equipped with: a water supply system ( 11 ) in which boiler water flows; ammonia addition equipment ( 12 ) that adds an ammonia solution to the boiler water; a pH measurement device ( 14 ) that measures the pH of the boiler water; and a control device ( 15 ). When the boiler water is heated the control device ( 15 ) controls the ammonia addition equipment ( 12 ) such that the pH of the boiler water is within a preservation pH range, and controls the ammonia addition equipment ( 12 ) such that the pH of the boiler water is within the preservation pH range before the flow of the boiler water in the water supply system ( 11 ) is stopped. At this time, a given pH within the preservation pH range is greater than a given pH within the operating pH range. With such a boiler, corrosion of the water supply system ( 11 ) can more easily be prevented than when the water supply system ( 11 ) is charged with preservation boiler water containing hydrazine.

TECHNICAL FIELD

The present invention relates to a boiler operation method and a boiler,and more particularly relates to a boiler operation method and a boilerused when preserving a water supply system through which boiler water iscirculated.

BACKGROUND ART

Boiler and steam turbine power plant, gas turbine and (heat recoverysteam generator) steam turbine combined cycle power plant, and the likehave water supply systems through which boiler water is circulated forgenerating steam (water vapor), but integrated coal gasificationcombined cycle (IGCC) power plants have many water supply systems forgenerating steam. An integrated coal gasification combined cycle powerplant includes a gasifier, a gas cooler, a gas turbine section, a heatrecovery steam generator, a steam turbine section, and a generator. Thegasifier generates combustible raw syngas from the gasification ofpulverized coal. The gas cooler cools the raw syngas. The gas turbinesection generates high temperature high pressure combustion gas bycombustion of the cooled raw syngas, thereby generating rotationalpower. The heat recovery steam generator recovers thermal energy fromthe exhaust gas from the gas turbine section, to generate high pressuresteam. The steam turbine section generates rotational power using thesteam. The generator converts the rotational power generated by the gasturbine section and the steam turbine section into electrical power.

The gas cooler and the heat recovery steam generator include watersupply systems through which boiler water is circulated. The gas coolercools the raw syngas generated by the gasifier and the heat recoverysteam generator cools the exhaust gas discharged from the gas turbinesection by circulating boiler water through the water supply systems. Inaddition, the gas cooler and the heat recovery steam generator heat theboiler water and generate steam supplied to the steam turbine section,by circulating the boiler water through the water supply systems.

Meanwhile, during periodic inspection when the operation of theintegrated coal gasification combined cycle power plant is stopped andthe equipment preservation time is long, the boiler water is dischargedwhen it is necessary to change the piping or the like of the watersupply system. However, when the boiler water is preserved withoutdischarging it in order to rapidly restart the power plant, it isdesirable to prevent corrosion of the metallic components such as theinside of the piping of the water supply systems and the like.

CITATION LIST Patent Literature

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2004-323954A

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2003-39084A

Patent Document 3: Japanese Unexamined Patent Application PublicationNo. H44-83592A

SUMMARY OF INVENTION Technical Problem

The occurrence of corrosion in the inside of piping and the like can bereduced by filling the water supply system with preserved water thatcontains hydrazine during the preservation period when operation of thepower plant is stopped and the boiler water is not discharged while theequipment is being preserved to enable rapid restarting. However, it isknown that hydrazine has an adverse effect on health, so it is necessaryto take care when handling it (see Patent Documents 1, 2, and 3). It isdesirable that corrosion of the metal members of the water supply systembe reduced more easily and over a longer period of time.

It is an object of the present invention to provide a boiler operationmethod and a boiler in which corrosion of the water supply systemthrough which the boiler water flows is easily reduced.

Solution to Problem

The boiler operation method according to a first aspect of the presentinvention is executed using a water supply system of a boiler. Theboiler includes the water supply system through which the boiler waterto be heated flows, and ammonia addition equipment configured to addammonia to the boiler water to adjust the pH of the boiler water. Theboiler operation method according to the present invention includes:measuring a pH of the boiler water; passing the boiler water through thewater supply system when the pH is within an operational pH range sothat the boiler water is heated upon operating the boiler; controllingthe ammonia addition equipment so that ammonia is added to the boilerwater until the pH is within a preservation pH range upon stopping theboiler; and stopping the flow of the boiler water in the water supplysystem when the pH is within the preservation pH range. At this time, adiscretionary pH within the preservation pH range is equal to or greaterthan a discretionary pH within the operational pH range.

According to this boiler operation method, by filling the water supplysystem with boiler water having a pH within the preservation pH range,it is possible to reduce corrosion of the water supply system for alonger period of time during preservation of the equipment when theoperation of the power plant has stopped compared with filling the watersupply system with boiler water having a pH within the operational pHrange. In addition, ammonia can normally be handled more easily comparedwith hydrazine. Therefore, this boiler operation method can more easilyprevent corrosion of the water supply system compared with filling thewater supply system with preservation boiler water that containshydrazine.

The boiler operation method according to the first aspect furtherincludes passing the boiler water through the water supply system whenthe pH is within the operational pH range so that the boiler water isheated, upon restarting operation of the boiler after the flow of theboiler water in the water supply system has been stopped.

According to this boiler operation method, the pH of the preservationboiler water is within the operational pH range, so it is possible torestart the boiler more easily and in a shorter period of time by usingthe preservation boiler water as it is as operation boiler water.

The boiler operation method according to the first aspect furtherincludes referring to a table of a plurality of preservation periodsmapped to a plurality of preservation pH ranges, and introducing thepreservation pH range corresponding to the period of time that a powerplant is stopped and boiler water is not flowing through the watersupply system, from among the plurality of preservation pH ranges. Atthis time, a lower limit of a first preservation pH range correspondingto a first period from among the plurality of preservation pH ranges isgreater than a lower limit of a second preservation pH rangecorresponding to a second period that is longer than the first periodfrom among the plurality of preservation pH ranges.

According to this boiler operation method, it is possible to add anappropriate quantity of ammonia to the boiler water, and moreappropriately reduce corrosion of the water supply system duringpreservation of the equipment.

The boiler according to a second aspect of the present inventionincludes: a water supply system through which boiler water to be heatedflows; ammonia addition equipment configured to add ammonia to theboiler water; a pH measurement device configured to measure the pH ofthe boiler water; and a control device configured to control the ammoniaaddition equipment. Upon operating the boiler, the control deviceincludes a control circuit for normal operation configured to controlthe ammonia addition equipment so that the pH is within an operationalpH range when the boiler water is flowing through the water supplysystem so that the boiler water is heated, and a control circuit forpreservation period configured to control the ammonia addition equipmentso that, upon stopping the boiler, the pH is within the preservation pHrange before stopping the flow of the boiler water through the watersupply system. At this time, a discretionary pH within the preservationpH range is equal to or greater than a discretionary pH within theoperational pH range.

With this boiler, it is possible to further reduce corrosion of thewater supply system by filling the water supply system with boiler waterhaving a pH within the preservation pH range compared with filling thewater supply system with boiler water having a pH within the operationalpH range. In addition, ammonia can normally be handled more easilycompared with hydrazine. Therefore, with this boiler, corrosion of thewater supply system during equipment preservation can be more easilysuppressed compared with filling the water supply system withpreservation boiler water that contains hydrazine.

A gas cooler according to a third aspect of the present inventionincludes a flow path through which raw syngas generated by gasificationof a carbonaceous solid fuel with an oxidant, and a flow path (boilerwater circulation system) through which supply water flows. At thistime, the water supply system heats the boiler water using the heat ofthe raw syngas.

This gas cooler can more easily suppress corrosion of the water supplysystem during equipment preservation when a power plant is stopped.

A heat recovery steam generator according to a fourth aspect of thepresent invention includes a flow path through which exhaust gasdischarged from a gas turbine flows, and a flow path (boiler watercirculation system) through which supply water flows. The water supplysystem heats the boiler water using the heat of the exhaust gas.

This heat recovery steam generator can more easily prevent corrosion ofthe water supply system during equipment preservation when the powerplant is stopped.

An integrated coal gasification combined cycle power plant according toa fifth aspect of the present invention includes: the heat recoverysteam generator according to the present invention; a gasifierconfigured to generate raw syngas by gasification of a carbonaceoussolid fuel; a gas turbine configured to discharge exhaust gas bygenerating power using the raw syngas; and a steam turbine configured togenerate power using steam. At this time, the steam is generated by thewater supply system by heating the boiler water using the heat of theraw syngas and using the heat of the exhaust gas.

This integrated coal gasification combined cycle power plant can moreeasily suppress corrosion of the water supply system during equipmentpreservation when the power plant is stopped.

Advantageous Effect of Invention

The boiler operation method and the boiler according to the presentinvention can easily reduce corrosion of the water supply system duringequipment preservation by filling the water supply system with boilerwater having a pH higher than the pH of the boiler water circulatedduring operation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating the configuration of anintegrated coal gasification combined cycle power plant.

FIG. 2 is a schematic view illustrating the configuration of a boilerwater circulating system.

FIG. 3 is a block diagram illustrating a control device.

FIG. 4 is a flow illustrating a boiler preservation method of acomparative example.

FIG. 5 is a graph showing the relationship between pH and corrosion.

DESCRIPTION OF EMBODIMENTS

A description of the embodiments of the boiler according to the presentinvention will be described below with reference to the drawings. Awater supply system portion of the boiler is used in an integrated coalgasification combined cycle power plant 10, as illustrated in FIG. 1.The integrated coal gasification combined cycle power plant 10 includesa gasifier 1, a gas cooler 2, a gas turbine 3, a heat recovery steamgenerator 5, a steam turbine 6, a generator 7, and a condenser 8. Thegasifier 1 generates combustible high temperature raw syngas frompulverized coal obtained by pulverizing coal as carbonaceous solid fuelsupplied from outside the power plant, and air (or oxygen) as anoxidant. The gas cooler 2 generates cooled raw syngas from the hightemperature raw syngas generated by the gasifier 1. The gas cooler 2generates high temperature high pressure steam from the boiler watergenerated by the condenser 8, by heat exchange when cooling the hightemperature raw syngas.

The gas turbine 3 generates rotational power using the cooled raw syngasgenerated by the gas cooler 2, and discharges high temperature exhaustgas. The heat recovery steam generator 5 generates high temperature highpressure steam from the boiler water generated by the condenser 8, byheat exchange when cooling the high temperature exhaust gas dischargedfrom the gas turbine 3. The steam turbine 6 generates rotational powerusing the steam generated by the gas cooler 2 and the steam generated bythe heat recovery steam generator 5, and discharges exhaust steam. Thegenerator 7 generates electrical power using the rotational powergenerated by the gas turbine 3 and the rotational power generated by thesteam turbine 6. The condenser 8 generates water from the exhaust steamdischarged from the steam turbine 6 to produce boiler water.

FIG. 2 illustrates a water supply (circulation) system portion of thegas cooler 2. The gas cooler 2 includes a water supply (circulation)system 11, ammonia addition equipment 12, a pH measurement device 14,and a control device 15, and includes a raw syngas flow path a. The rawsyngas generated by the gasifier 1 flows through the raw syngas flowpath a. The water supply system 11 includes a steam drum 16, a pluralityof downcast pipes 17, a header 18, and a plurality of heat transferpipes 19. The steam drum 16 is formed into a vessel formed from steelbased material (hereinafter, referred to as “steel”). The steam drum 16is connected to the condenser 8 via a pipe line 30 so that boiler watergenerated in the condenser 8 is supplied to the inside of the steam drum16. The steam drum 16 is connected to the steam turbine 6 via a pipeline 31 so that steam generated in the inside of the steam drum 16 issupplied to the steam turbine 6. The steam drum 16 is also connected tothe plurality of downcast pipes 17 so that the boiler water accumulatedin the inside of the steam drum 16 is supplied to the plurality ofdowncast pipes 17.

Each of the plurality of downcast pipes 17 is formed from steel and isformed as a flow path through which boiler water supplied from the steamdrum 16 flows. Each of the plurality of downcast pipes 17 is connectedto the header 18 so that the boiler water is supplied to the header 18.The header 18 is formed from steel and is formed as a header into whichthe boiler water supplied from the plurality of downcast pipes 17 merge.The header 18 is connected to the plurality of heat transfer pipes 19 sothat the boiler water is supplied to the plurality of heat transferpipes 19.

The plurality of heat transfer pipes 19 is formed from steel and isformed as the flow path through which the boiler water supplied from theheader 18 flows. The plurality of heat transfer pipes 19 is disposedwithin the flow path a of the raw syngas, so that the pipes are heatedby the heat of the raw syngas generated by the gasifier 1. The pluralityof heat transfer pipes 19 is connected to the steam drum 16 so that theboiler water supplied from the header 18 is supplied to the steam drum16.

The ammonia addition equipment 12 is electrically connected to thecontrol device 15 so as to enable transfer of information andaccumulates ammonia solution. The ammonia addition equipment 12 iscontrolled by the control device 15 to supply ammonia solution to thepipe line 30 so that ammonia solution is added to the boiler watersupplied to the steam drum 16 from the condenser 8.

The pH measurement device 14 is electrically connected to the controldevice 15 so as to enable transfer of information. The pH measurementdevice 14 is controlled by the control device 15 to measure the pH ofthe boiler water accumulated in the steam drum 16 either atpredetermined intervals or continuously.

The control device 15 is a computer that includes a CPU, a memorydevice, a memory drive, a communication device, and an interface, thatare not illustrated on the drawings.

The interface outputs information generated by external equipmentconnected to the control device 15 to the CPU, and outputs informationgenerated by the CPU to the external equipment. The external equipmentincludes the ammonia addition equipment 12 and the pH measurement device14.

The computer programs installed in the control device 15 are formed froma plurality of computer programs to make the control device 15 realize aplurality of functions, as illustrated in FIG. 3. The plurality offunctions includes a control circuit for normal operation 21 and acontrol circuit for preservation period 22.

During operation of the gasifier 1 and the gas cooler 2, the pHmeasurement device 14 measures the pH of the boiler water accumulated inthe steam drum 16 at least once. The control circuit for normaloperation 21 stores in advance an operational pH range in the memorydevice. The set value in the operational pH range is, for example, 9.7.The control circuit for normal operation 21 also controls the ammoniaaddition equipment 12 so that the pH of the boiler water accumulated inthe steam drum 16 is within the operational pH range. In other words,the control circuit for normal operation 21 controls the ammoniaaddition equipment 12 so that when the pH of the boiler water is lessthan the set value in the operational pH range, ammonia solution issupplied to the pipe line 30. The control circuit for normal operation21 controls the ammonia addition equipment 12 so that when the pH of theboiler water is equal to or greater than the set value in theoperational pH range, the ammonia solution is not supplied to the pipeline 30.

The control circuit for preservation period 22 stores in advance apreservation pH range in the memory device. The lower limit of thepreservation pH range is equal to or greater than the set value in theoperational pH range, for example, 9.7. The control circuit forpreservation period 22 also controls the ammonia addition equipment 12so that the pH of the boiler water accumulated in the steam drum 16 iswithin the preservation pH range. In other words, the control circuitfor preservation period 22 controls the ammonia addition equipment 12 sothat when the pH of the boiler water accumulated in the steam drum 16 islower than the lower limit of the preservation pH range, ammoniasolution is supplied to the pipe line 30. The control circuit forpreservation period 22 controls the ammonia addition equipment 12 sothat when the pH of the boiler water accumulated in the steam drum 16 isgreater than the lower limit of the preservation pH range, ammoniasolution is not supplied to the pipe line 30.

The heat recovery steam generator 5 includes a water supply system thatis not illustrated on the drawings. The water supply system is formedsimilar to the water supply system 11, in other words, it includes asteam drum, a plurality of downcast pipes, a header, and a plurality ofheat transfer pipes. The steam drum is formed into a vessel formed fromsteel. The steam drum is connected to the pipe line 30, and connected tothe pipe line 31. The steam drum is also connected to the plurality ofdowncast pipes so that the boiler water accumulated in the inside of thesteam drum is supplied to the plurality of downcast pipes.

Each of the plurality of downcast pipes is formed from steel and isformed as a flow path through which boiler water supplied from the steamdrum flows. Each of the plurality of downcast pipes is connected to theheader so that the boiler water is supplied to the header. The header isformed from steel, and formed as a vessel in which boiler water suppliedfrom the plurality of downcast pipes is accumulated. The header isconnected to the plurality of heat transfer pipes so that the boilerwater is supplied to the heat transfer pipes.

The plurality of heat transfer pipes is formed from steel and is andformed as a flow path through which the boiler water supplied from theheader flows. The plurality of heat transfer pipes is disposed in theflow path through which the exhaust gas flows, so that it is heated bythe heat of the exhaust gas discharged from the gas turbine 3. Theplurality of heat transfer pipes is connected to the steam drum so thatthe boiler water supplied from the header is supplied to the steam drum.

The embodiment of the boiler operation method according to the presentinvention is implemented using the integrated coal gasification combinedcycle power plant 10, and includes normal operation, preservationoperation, and restart operation.

In normal operation, the gasifier 1 generates combustible hightemperature raw syngas using air (or oxygen) supplied from externalequipment, by pulverizing and burning coal as carbonaceous solid fuelsupplied from external equipment. The gas cooler 2 generates cooled rawsyngas by heat exchange using the boiler water generated by thecondenser 8 so as to cool the high temperature raw syngas generated bythe gasifier 1. At this time, the gas cooler 2 generates hightemperature high pressure steam by heat exchange using the heat of thehigh temperature raw syngas generated by the gasifier 1 to heat theboiler water.

The gas turbine 3 generates high temperature high pressure exhaust gasby burning the cooled raw syngas generated by the gas cooler 2. The gasturbine 3 generates rotational power using the kinetic energy of theexhaust gas, and discharges the exhaust gas. The heat recovery steamgenerator 5 generates cooled exhaust gas by heat exchange using theboiler water generated by the condenser 8 to cool the high temperatureexhaust gas discharged from the gas turbine 3. At this time, the heatrecovery steam generator 5 generates high temperature high pressuresteam by heat exchange using the heat of the high temperature exhaustgas discharged from the gas turbine 3 to heat the boiler water generatedby the condenser 8.

The steam turbine 6 generates rotational power using the kinetic energyof the high temperature high pressure steam generated by the gas cooler2 and the kinetic energy of the high temperature high pressure steamgenerated by the heat recovery steam generator 5, and discharges exhauststeam. The generator 7 generates power using the rotational powergenerated by the gas turbine 3 and the rotational power generated by thesteam turbine 6. The condenser 8 carries out heat exchange to cool theexhaust steam discharged by the steam turbine 6 to generate water asboiler water, and supplies the boiler water to the gas cooler 2 and theheat recovery steam generator 5 via the pipe line 30.

At this time, the pH measurement device 14 measures the pH of the boilerwater accumulated in the steam drum 16 of the gas cooler 2. The pHmeasurement device 14 transmits the measured pH to the control device15. When the measured pH is equal to the set value in the operational pHrange, or the measured pH is greater than the set value, the controldevice 15 controls the ammonia addition equipment 12 to stop theaddition of ammonia solution to the boiler water supplied to the steamdrum 16 from the condenser 8. When the measured pH is lower than the setvalue in the operational pH range that is set in advance, the controldevice 15 controls the ammonia addition equipment 12 to add ammoniasolution to the boiler water supplied to the steam drum 16 from thecondenser 8.

The gas cooler 2 circulates the boiler water supplied from the condenser8 to the water supply system 11 via the pipe line 30 to generate steamfrom the boiler water. In other words, the plurality of downcast pipes17 supplies the boiler water accumulated in the steam drum 16 to theheader 18. In the header 18, the boiler water supplied from theplurality of downcast pipes 17 merge. The plurality of heat transferpipes 19 carries out heat exchange so that the boiler water that hasmerged at the heating pipe header 18 is heated using the heat of thehigh temperature raw syngas generated by the gasifier 1, and the heatedboiler water is supplied to the steam drum 16. The steam drum 16accumulates the boiler water supplied from the condenser 8 via the pipeline 30 and the boiler water heated by the plurality of heat transferpipes 19. In addition, in the steam drum 16, liquid-vapor separation ofthe accumulated heated boiler water is carried out and the liquid-vaporseparated steam is supplied to the steam turbine 6.

The preservation operation is implemented immediately before stoppingthe integrated coal gasification combined cycle power plant 10 forperiodic inspection, maintenance, and the like. Immediately beforestopping the integrated coal gasification combined cycle power plant 10,the control device 15 first measures the pH of the boiler wateraccumulated in the steam drum 16 using the pH measurement device 14.When the measured pH is lower than the lower limit of the preservationpH range, the control device 15 controls the ammonia addition equipment12 to supply ammonia solution to the pipe line 30. When the measured pHis equal to or greater than the lower limit of the preservation pHrange, the control device 15 controls the ammonia addition equipment 12to stop the supply of ammonia solution to the pipe line 30.

After it has been confirmed that the measured pH is equal to or greaterthan the lower limit of the preservation pH range, operation of theintegrated coal gasification combined cycle power plant 10 is stopped.The water supply system 11 stops circulating the boiler water as aresult of stopping the operation of the integrated coal gasificationcombined cycle power plant 10. In addition, after stopping circulationof the boiler water, oxygen is discharged from the spaces filled by gaswithin the water supply system 11 and the spaces are filled withpressurized nitrogen by injecting nitrogen under pressure.

FIG. 5 is a graph showing the relationship between pH and corrosion.Test specimens were immersed in an ammonia solution with different pHwithin a sealed container under test conditions of oxygen saturation(25° C., 8 mg/L) and room temperature, and from the test results, it wasdetermined whether or not there was corrosion by inspecting the surface,and the corrosion area was determined as a percentage of the total area.When steel is immersed in ammonia solution, the higher the pH of theammonia solution, the more the corrosion speed is reduced, so it ispossible to suppress corrosion in the steel over a longer period oftime. Therefore, according to this preservation operation, it ispossible to achieve a greater reduction in the corrosion of the watersupply system 11 during preservation of the equipment when theintegrated coal gasification combined cycle power plant 10 is stopped,by filling the water supply system 11 with boiler water having pH withinthe preservation pH range compared with filling the water supply system11 with boiler water having pH within the operational pH range. As aresult, according to this preservation operation, the water supplysystem 11 is able to be preserved in a manner that it does not corrodeduring preservation of the equipment when the integrated coalgasification combined cycle power plant 10 is stopped.

The restart operation is implemented after implementation of thepreservation operation, after the integrated coal gasification combinedcycle power plant 10 has been stopped for a predetermined period oftime. In the restart operation, the operation of the integrated coalgasification combined cycle power plant 10 is restarted and normaloperation is implemented without removing the boiler water from thewater supply system 11 and without re-supplying boiler water thatsatisfies the water quality for normal operation, unlike theconventional method of initiating restart after filling the water supplysystem 11 with preserved water that contains hydrazine during theequipment preservation period.

According to this restart operation, it is possible to shorten the timerequired for restarting the integrated coal gasification combined cyclepower plant 10 and restart in a shorter period of time than for aconventional restart operation, by not replacing the boiler water havinga pH within the preservation pH range with boiler water having a pHwithin the operational pH range.

In a comparative example of the boiler operation method, as anembodiment of a conventional equipment preservation method, a similarboiler operation method as the embodiment described above is implementedusing the integrated coal gasification combined cycle power plant 10,the preservation operation in the embodiment as described above isreplaced with another preservation operation, and the restart operationin the embodiment as described above is replaced with another restartoperation.

In the preservation operation, after the integrated coal gasificationcombined cycle power plant 10 has been stopped, the boiler water isremoved from the water supply system 11I as illustrated in FIG. 4 (StepS1). After the boiler water has been removed, the water supply system 11is filled with preserved water. The preserved water contains 50 mg/L ofhydrazine. After filling with the preserved water, the air that containsoxygen is discharged from the spaces filled with gas within the watersupply system 11, and the spaces are filled with pressurized nitrogen byinjecting with nitrogen under pressure (Step S2).

According to this preservation operation, it is possible to suppress thecorrosion of the steel from which the water supply system 11 isconfigured for a long period of time by filling the water supply system11 with the preserved water that contains 50 mg/L of hydrazine while theintegrated coal gasification combined cycle power plant 10 is stopped.

In the restart operation, before restarting the integrated coalgasification combined cycle power plant 10, the preserved water thatcontains hydrazine at a higher concentration than that of hydrazinesuitable for normal operation is removed from the water supply system 11(Step S3). After removal of the preserved water, the water supply system11 is filled with boiler water (Step S4). The boiler water is formedfrom water that does not contain hydrazine. After filling the watersupply system 11 with boiler water, operation of the integrated coalgasification combined cycle power plant 10 is restarted, and normaloperation is implemented.

According to this restart operation of the conventional embodiment, itis possible to appropriately operate at normal operation the integratedcoal gasification combined cycle power plant 10 by circulating boilerwater that does not contain hydrazine in the water supply system 11.

Meanwhile, ammonia is normally easier to obtain compared with hydrazine,and can be handled more easily.

In addition, in the restart operation after equipment preservation inthe embodiment as described above, the boiler water is not removed fromthe water supply system 11 before preservation of the water supplysystem 11. In other words, by restarting operation without removing theboiler water having pH within the preservation pH range as a result ofinjecting ammonia solution, it is possible to implement the restartoperation in a shorter period of time and at lower cost due to theboiler water not being discarded, compared with the restart operationafter equipment preservation of the comparative example. In the restartoperation according to the embodiment as described above, by notremoving the boiler water that filled the water supply system 11 duringequipment preservation, it is possible to omit the step of filling thewater supply system 11 with preserved water that contains hydrazineafter removal of the boiler water from the water supply system 11 inorder to start the equipment preservation after stopping the integratedcoal gasification combined cycle power plant 10. In addition, it ispossible to omit the step of filling the water supply system 11 withboiler water after removal of the preserved water that containshydrazine, in order to implement the restart. It is possible toimplement the restart operation in the embodiment as described above ina shorter period of time compared with the restart operation of thecomparative example. Therefore, according to the boiler operation methodof the embodiment as described above, it is possible to stop theintegrated coal gasification combined cycle power plant 10 in a shorterperiod of time and to restart it in a shorter period of time comparedwith the boiler operation method according to the comparative example.

The operation executed by the control device 15 can be executed by auser. In other words, the pH of the boiler water accumulated in thesteam drum 16 of the gas cooler 2 is measured by the user by controllingthe pH measurement device 14. By operating the ammonia additionequipment 12, ammonia solution is added to the pipe line 30 and theaddition of the ammonia solution is stopped. In this case also, it ispossible to easily prevent corrosion in a similar way as the boileroperation method according to the embodiment as described above, and theintegrated coal gasification combined cycle power plant 10 can bestopped in a shorter period of time and can be restarted in a shorterperiod of time. In other words, the gas cooler 2 and the heat recoverysteam generator include a boiler, so the above effect can be exhibited.The boiler includes the water supply system through which the boilerwater to be heated flows, ammonia addition equipment that adds ammoniato the boiler water, and the pH measurement device that measures the pHof the boiler water.

In another embodiment of the boiler according to the present invention,the control circuit for preservation period 22 of the embodiment asdescribed above is replaced with another control circuit forpreservation period. In the control circuit for preservation period, aplurality of preservation pH ranges corresponding to a plurality ofpreservation periods is stored in advance in the memory device. Each ofthe plurality of preservation pH ranges has a lower limit that is equalto or greater than the set value in the operational pH range. Forexample, according to the test results shown in FIG. 5, the lower limitof the preservation pH range corresponding to a period equal to or lessthan 24 hours may be 9.5. The lower limit of the preservation pH rangecorresponding to a period equal to or less than 72 hours may be 9.7. Thelower limit of the preservation pH range corresponding to a period from4 days to 7 days may be 9.8. The lower limit of the preservation pHrange corresponding to a period from 7 days to 14 days may be 9.9. Thelower limit of the preservation pH range corresponding to a period from15 days to 30 days may be 10. The longer the preservation period, thehigher the corresponding lower limit of the preservation pH range.

Also, for example, in a high temperature strong alkaline environment (pH11 or higher), preferably, the upper limit of the preservation pH isless than pH 11, because of the possibility of alkaline corrosion evenin steel that is normally strongly alkali resistant. However, this isnot a limitation.

When a user inputs a preservation period into the control device 15, acontrol circuit for preservation operation calculates a preservation pHrange corresponding to the preservation period from the plurality ofpreservation pH ranges. The control circuit for preservation operationcontrols the pH measurement device 14 to measure the pH of the boilerwater accumulated in the steam drum 16. The control circuit forpreservation period controls the ammonia addition equipment 12 so thatthe pH of the boiler water accumulated in the steam drum 16 is withinthe preservation pH range. Also, the ammonia addition equipment 12 maybe operated by a manual operation, and is not limited to calculating thepreservation pH range corresponding to the preservation period, andcontrolling the ammonia addition equipment 12.

The integrated coal gasification combined cycle power plant thatincludes such a control circuit for preservation period can more easilysuppress the corrosion of the water supply system 11, can stop in ashorter period of time, and can restart in a shorter period of time,similar to the integrated coal gasification combined cycle power plant10 according to the embodiment as described above.

FIG. 5 shows the relationship between pH of the preserved water andcorrosion. This relationship shows the pH of the preserved water inwhich test specimens formed from the steel are immersed, and shows thecorrosion area corresponding to the number of days elapsed afterimmersing the test specimens in the preserved water. The corrosion areashows the area of the region that is corroded after the elapsed time asa percentage of the area of the surface of the test specimen in contactwith the preserved water. Also, this relationship shows the progressionof corrosion with time. In addition, this relationship shows that thehigher the pH of the preserved water, the longer the time at whichcorrosion of the test specimens starts is delayed. Therefore, thisrelationship shows that the greater the pH of the boiler water fillingthe water supply system 11 during preservation, the longer the period oftime that corrosion can be prevented.

Therefore, with the integrated coal gasification combined cycle powerplant that includes such a control circuit for preservation period, byincreasing the lower limit of the preservation pH range the longer thepreservation period when the integrated coal gasification combined cyclepower plant is stopped, it is possible to reduce the addition quantityof ammonia used for preservation of the water supply system 11, andappropriately prevent corrosion of the water supply system 11.

Note that the preservation pH range can be replaced with anotherpreservation pH range whose lower limit is 9.5. The lower limit of thepreservation pH range is equal to the set value in the operational pHrange, or, is greater than the set value in the operational pH range.

REFERENCE SIGNS LIST

-   1 Gasifier-   2 Gas cooler-   3 Gas turbine-   5 Heat recovery steam generator-   6 Steam turbine-   10 Integrated coal gasification combined cycle power plant-   11 Water supply system-   12 Ammonia addition equipment-   14 pH measurement device-   15 Control device-   21 Control circuit for normal operation-   22 Control circuit for preservation period

1. A boiler operation method implemented using a boiler that includes awater supply system through which boiler water flows, and ammoniaaddition equipment configured to add ammonia solution to the boilerwater, the method comprising the steps of: measuring a pH of the boilerwater; passing the boiler water through the water supply system when thepH is within an operational pH range so that the boiler water is heated,upon operating the boiler; controlling the ammonia addition equipment sothat ammonia solution is added to the boiler water until the pH iswithin a preservation pH range, upon stopping the boiler; and stoppingthe flow of the boiler water in the water supply system when the pH iswithin the preservation pH range, a discretionary pH within thepreservation pH range being equal to or greater than a discretionary pHwithin the operational pH range.
 2. The boiler operation methodaccording to claim 1, further comprising passing the boiler waterthrough the water supply system when the pH is within the operational pHrange so that the boiler water is heated, upon restarting operation ofthe boiler after the flow of the boiler water in the water supply systemhas been stopped.
 3. The boiler operation method according to claim 1,further comprising referring to a table of a plurality of preservationperiods mapped to a plurality of preservation pH ranges, and introducingthe preservation pH range corresponding to the period of time that apower plant is stopped and boiler water is not flowing through the watersupply system, from among the plurality of the preservation pH ranges,wherein a lower limit of a first preservation pH range corresponding toa first period from among the plurality of preservation pH ranges isgreater than a lower limit of a second preservation pH rangecorresponding to a second period that is longer than the first periodfrom among the plurality of preservation pH ranges.
 4. The boileroperation method according to claim 3, wherein the lower limit of thefirst preservation pH range and the lower limit of the secondpreservation pH range have values within a range of 9.5 to
 10. 5. Aboiler, comprising: a water supply system through which boiler waterflows; ammonia addition equipment configured to add ammonia solution tothe boiler water; a pH measurement device configured to measure a pH ofthe boiler water; and a control device, upon operating the boiler, thecontrol device including a control circuit for normal operationconfigured to control the ammonia addition equipment so that the pH iswithin a operational pH range when the boiler water is flowing throughthe water supply system so that the boiler water is heated, and acontrol circuit for preservation period configured to control theammonia addition equipment so that the pH is within the preservation pHrange before stopping the flow of the boiler water through the watersupply system upon stopping the boiler, a discretionary pH within thepreservation pH range being equal to or greater than a discretionary pHwithin the operational pH range.
 6. A gas cooler, comprising: the boilerdescribed in claim 5; and a flow path through which raw syngas generatedby gasification of a carbonaceous solid fuel flows, the water supplysystem heating the boiler water using heat of the raw syngas.
 7. A heatrecovery steam generator, comprising: the boiler described in claim 5;and a flow path through which exhaust gas discharged from a gas turbineflows, the water supply system heating the boiler water using heat ofthe exhaust gas.
 8. An integrated coal gasification combined cycle powerplant, comprising: the boiler according to claim 5; a gasifierconfigured to generate raw syngas by gasification of a carbonaceoussolid fuel; a gas turbine configured to discharge exhaust gas bygenerating power using the raw syngas; and a steam turbine configured togenerate power using steam, the steam being generated by the watersupply system by heating the boiler water using heat of the raw syngasand using heat of the exhaust gas.
 9. The boiler operation methodaccording to claim 2, further comprising referring to a table of aplurality of preservation periods mapped to a plurality of preservationpH ranges, and introducing the preservation pH range corresponding tothe period of time that a power plant is stopped and boiler water is notflowing through the water supply system, from among the plurality of thepreservation pH ranges, wherein a lower limit of a first preservation pHrange corresponding to a first period from among the plurality ofpreservation pH ranges is greater than a lower limit of a secondpreservation pH range corresponding to a second period that is longerthan the first period from among the plurality of preservation pHranges.